Hi all
anyone know how to pinpoint the source of this code. just had ebcm rebuilt and shop saying it's still the ebcm.

 

I'm guessing based on your description this is a U0121 issue?

Neal

 

DTC C0121

Circuit Description

The solenoid valve relay supplies power to the solenoid valve coils in the EBCM. The solenoid valve relay,
located in the EBCM, is activated whenever the ignition switch is in the RUN position and no faults are present.
The solenoid valve relay remains engaged until the ignition is turned OFF or a failure is detected.

Conditions for Running the DTC

The ignition switch is in the ON position.

Conditions for Setting the DTC

DTC C0121 will set anytime the solenoid valve relay is commanded on and the EBCM does not see
battery voltage at the solenoid valves.

DTC C0121 will set anytime the EBCM commands the solenoid valve relay off and battery voltage is still
present at the solenoid valves.

Action Taken When the DTC Sets

If equipped, the following actions occur:

The EBCM disables the ABS/TCS/DRP for the duration of the ignition cycle.

A malfunction DTC is set.

The ABS indicator turns ON.

The TRAC Off indicator turns ON.

The Red BRAKE Warning indicator could turn on.

Conditions for Clearing the DTC

The condition for the DTC is no longer present and the DTC is cleared with a scan tool.

The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC
is not detected in 100 consecutive drive cycles.

It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.

Thoroughly inspect any circuitry that may be causing the complaint for the following conditions:

Backed out terminals

Improper mating

Broken locks

Improperly formed or damaged terminals

Poor terminal-to-wiring connections

Physical damage to the wiring harness

The following conditions may cause an intermittent malfunction:

A poor connection

Rubbed-through wire insulation

A broken wire inside the insulation

The solenoid valve relay is an integral part of the EBCM and is not serviced separately.

 

More history would be helpful:-

• What prompted you to get the ECBM serviced in the 1st instance?
• Are the latest symptoms the same?
• What was happing before it failed?

I'm assuming after the module was rebuilt it wasn't tested electrically, is this correct?

It's not a fun job removing the module, but based on hummerz data it looks like there are two possibilities:-

1. The ECBM actually is faulty.
2. Or, as the data suggests, it's an electrical fault.

According to my diagram there are 3 key voltage sources going into the module:-

• Pin 9 (Pink wire) this is Hot when the ignition is on. Check the 15A ECC/ECM Fuse (highly possibly related)
• Pin 13 (Red) this is Hot all the time and connects to the 60A ABS Fuse.
• Pin 14 (Orange) is Hot all the time and connects to the 30A SEO B2 Fuse
• All the Fuses are located under the hood.

At least Pin 13 and/or Pin 14 must be Hot otherwise the module would not communicate (sorry not sure which)

Check all the above fuses, check they all have voltage on with the ignition on.

The diagram shows IGN 1 Relay is related so check this (it may be the one mid-right below, not sure)


With the battery disconnected !
The connector to the module is relatively easy to access, I think it can be un-plugged whilst the ECBM in place. Pull the big white locking "tang" until the plug disengages (apologies if you already know this)

Inspect the cable connectors female pins, make sure they look clean and have not been "splayed" or damaged in any way. Gently "tug" on the above related wires and make sure they are firmly connected.
Use a mirror to check the ECBM pins, they too should look clean and not bent.
Take pictures of the cable connector pins, and ECBM pins reference.

Extend some multimeter leads and perform a low ohms continuity check between above 3 cable connector pins to their relevant fuses. They should all be just a fraction of an ohm (don't forget to account for the extended meter leads, measure these 1st)

Also check cable Pin 12 (Black) this is the 0V ground wire, it connects to the chassis, diagram says "At Right Frame Body Mount, Near Right Rear Door) Check the earth bond, check the continuity from Connector Pin 12 to chassis/Battery -VE, it MUST be low.

If the continuity checks are OK, reconnect the ECBM then reconnect the battery.
Double check you have voltage on all the above fuses with the ignition ON.

Best I can offer, if you have more data or need more info, please let us know.

 

ulthummer
How are you getting along, any progress?